Semiconductor devices are widely used in various industries such as electronic devices, cars and/or vehicles because of their small size, lightness, and low manufacture costs. An electric field transistor (hereinafter, referred to as a transistor) may be one of important components constituting semiconductor devices. Generally, a transistor may include a source, a drain, and a gate electrode. The source and the drain may be spaced apart from each other in a semiconductor substrate, and the gate electrode may be disposed over a channel region between the drain and the source. The source and the drain may be formed by implanting dopant ions into the semiconductor substrate. The gate electrode may be electrically insulated from the channel region by a gate oxide layer therebetween.
The transistors may be widely used as a switching component and/or components constituting a logic circuit in the semiconductor device. Recently, high speed transistors have been increasingly demanded. On the contrary, sizes of the transistors have been more reduced with high integration of semiconductor devices. Thus, a turn-on current of a transistor may be reduced and performance of the transistor may deteriorate, such that reliability of a semiconductor device may deteriorate. Additionally, an operating speed of the semiconductor device may be reduced. Therefore, various researches have been conducted for increasing the turn-on current of the transistor.
Source drain stressors may be used to increase the carrier mobility in the channel region of the MOS transistor. Tensile stressors may be used for an NMOS transistor and compressive stressors may be used for a PMOS transistor. Stressor materials may be epitaxial layers.